The invention relates to a method and plant for producing endless laminated veneer boards.
A method of this kind is disclosed by German Offenlegungsschrift 196 27 024. This method is based on the object of automatically and continuously assembling assemblies of layers of large-area veneer panels (or sheets) to give adequate mechanical interlinking, with the result that, given the subsequent continuous pressing operation, these veneer-assembly transitions have virtually the same physical strength properties in the finished laminated veneer boards, as the laminated veneer boards produced in accordance with the previous laminated veneer assemblies joined together in a sandwich construction. With this method, it is possible to produce laminate veneer boards of good quality if all the manufacturing and production parameters are matched to one another in an optimum manner and the plant operates accordingly. One disadvantage of this method is the high proportion of the costs accounted for by the plant.
According to another method that has been disclosed, the veneer panels are deposited in the appropriate laying position by means of a rolling belt. Here, the veneer panels are first of all moved into the deposition position by means of the rolling belt and are then unloaded as the belt projection moves back, as a result of which the veneer panel falls onto the conveyor belt or veneer assembly underneath it.
For a complete deposition cycle comprising the following steps:
a) taking over veneer panel onto a rolling belt, PA1 b) moving veneer panel into a deposition position and PA1 c) unloading and depositing veneer panel during return movement, it was previously possible to achieve cycle times of 5 s per veneer panel.
However, industrial-scale LVL production plants with a production capacity of about 250 m.sup.3 per day must achieve cycle times of at least 2.5 s per veneer panel in order to keep up with the competition. For this reason, the laying operation in the laying stations is carried out on two levels to enable the required 24 veneer panels per minute to be achieved at a laying cycle of 5 s per veneer panel per level.
However, one disadvantage of these multi-level laying stations is that the laid veneer assemblies from the two levels must then be combined to give a veneer-panel strand. This necessarily requires sloping conveyor belts and corresponding kinks. At the transition from the horizontal to the slope and vice versa, stretching and compression effects occur which deform the veneer-panel strand or displace the veneer panels relative to one another. Since the veneer panels are already glued at this point in time, the displacements and deformations occur at undefined locations and lead to a change in the lengths of overlap between the veneer panels. The length of overlap must not fall below a minimum length in order to achieve the required bending strengths in the finished boards. Accordingly, any overlap tolerances must be compensated for by increasing the length of overlap and this results in a commercial disadvantage due to increased use of material.
The large number of drive elements in these plants also entails considerable susceptibility to faults, which impairs the availability of the overall production line.